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I Quark and lepton charges

  1. Jun 17, 2016 #1
    Hello everyone,
    I'm sorry if it's a dumb question, I'm very new in self studying particle physics.
    May I ask when we associate a charge (i.e. positive or negative) to quark and lepton, is it only because of their attraction or repulsion toward each other? in other words, is it just to name one of their properties because the way they react to another particle's property?
    Thank you so much in advance.
     
  2. jcsd
  3. Jun 17, 2016 #2

    From our usual /classical world experiences we have attributed charge to a particle or body based on the its interaction with other bodies- so it’s a characteristic attribute and can not be associated with a ‘material’ picture .
    So ,you are right in saying <just to name one of their properties because the way they react to another particle's property?>

    Such as flow of charges are not like “fluid flow” but movement of particles or fields in space.

    The action at a distance between charges also is mediated by ‘particles’ which can be exchanged

    If we look from the basis of Field theory particles can be visualized as states (or quanta) of field quantum.

    When a field is invariant under some of transformations called a gauge transformation, then the associated particle is said to have charge which corresponds to that symmetry. This is where electric charge comes from, along with other types of charges such as color charges.

    A particle’s charge determines how it transforms under symmetry operations. (see Noether's Theorem.)
    Other intrinsic properties like "spin" also behaves like a spin-charge- if particles with well defined spins move then a 'spin-wave' can be built up.
     
  4. Jun 17, 2016 #3

    Jonathan Scott

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    Gold Member

    If you mean electric charge, then the charges on leptons can be assigned according to how they move in an electromagnetic field. Quarks are conceptual components which make up mesons and baryons, and their electric charges are assigned in such a way that their combinations to form the relevant mesons and baryons have the correct observed overall charge when added together. For this to work for baryons, the charges need to be fractional (plus or minus 1/3 or 2/3 of the elementary charge).

    Other quantum properties which may be called "charge" are assigned in such a way as to give the correct overall properties for the combinations of quarks which form the actual particles.
     
  5. Jun 29, 2016 #4
    Hello drvm,

    Thank you so much for your complete answer to my question. It gave me a lot of information and a new way of thinking about that. I appreciate it.
    Regards,
    Behrouz
     
  6. Jun 29, 2016 #5
    Dear Jonathan,

    Thanks for your response. I was looking for the meaning of 'Charge', not the way it is used in electricity or 'electrical' charge, but the reason behind the 'Negative' and 'positive' definitions for physical particles. I believe the second part of your answer is helping me in that case.
    Thanks again. I appreciate it.

    Regards,
    Behrouz
     
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